CBSE Sample Paper CHEMISTRY Class XII 2009


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Sample Paper – 2009
Class – XII
Subject –
Chemistry

Time-3 Hours Max.Mark-70

General Instruction:

1. All questions are compulsory.

2. Marks of each question are indicated against it.

3. Questions number 1 to 8 are very short answer questions and carry 1 mark each.

4. Questions numbers 9 to 18 are short answer questions and carry 2 marks each.

5. Question numbers 19 to 27 are also short answer questions and carry three marks each.

6. Question numbers 28 to 30 is long answer questions and carry five marks each.

7. Use log tables if necessary. Use of Calculators are not allowed.

1. In an fcc arrangement of A and B atoms ,where A atoms are at the corners of the unit cell and B atoms at the face centers, one of the A atoms is missing from one corner in each unit cell.What is the simplest formula of the compound? 1

2. What happens to the magnetic property of Fe3O4 at 850K? 1

3. 2g. each of 2 solutes A and B (molecular mass of A>B) are dissolved separately in 50g.each of the same solvent. Which will show greater elevation in Boiling point? Why?1

4. Osmotic pressure measurements are preferred over other colligative properties for molecular mass determination of polymers, why? 1

5. Why carboxylic acids do not give the characteristic reactions of carbonyl group? 1

6. Why do transition metals form interstitial compounds? 1

7. Write a chemical equation to illustrate Saytzev’s rule.1

8. An α-amino acid in alkaline medium is subjected to electrolysis. Predict the outcome. 1

9. A unit cell of NaCl has 4 formula units. Its edgelength is 0.504 nm. Calculate the density. (molecular mass of Nacl=58.5). 2

OR

Describe the following

a) Metal excess defect

b) Metal deficiency defect. 2

10. The emf of a cell corresponding to the reaction Zn(s)+2H+(aq)àZn2+(0.1M)+H2(g)(1atm) is 0.28 v at 250C. Calculate the pH of the solution at the hydrogen electrode.(E0 Zn2+/Zn =-0.76 V, E0 H+/H2 =0). 2

11. a) What happens when freshly prepared Fe(OH)3 is shaken with little amount of dilute FeCl3 solution?

b) Alum is added to purify water with suspended impurities. Why? 2

12. Write short notes on

a) Activity and selectivity of catalysts.

b) Shape selective catalysis. 1

13. A compound A with molecular formula C4H10O on oxidation form compound B which gives positive iodoform test. Compound (B) on reaction with CH3MgBr followed by hydrolysis gives C. C when treated with HBr gives a tertiary alkylhalide D. Identify A, B, C and D. 2

14. Give the IUPAC names of

a) (CH3)2C=C(Br)CH2OH

b) CH3CH2CH(Cl)CH(OH)CH(CH3)2. 2

15. Write short notes on

a) Gabriel phthalimide synthesis.

b) Hoffmann Bromamide reaction. 2

16. Convert

a) Benzyl chloride to 2-phenyl ethanamine.

b) Benzamide to phenyl isocynide. 2

17. i) Cr2+ is reducing while Mn3+ is oxidizing when both have d4 configuration. Why?

ii)Write balanced chemical equations for the oxidation of

a) Hydrogen sulphide to sulphur.

b) Ferrous salt to ferric salt

by potassium dichromate in acidic medium. 2

18. Discuss briefly the following properties of transition metals

a) variable oxidation states

b) ability to form coloured ions. 2 19. a)1.22 g. of benzoic acid (C6H5COOH) are added in 100g. acetone and 100g. benzene. Boiling point of solution in acetone increases by 0.170C while that in benzene increases by 0.130C. Calculate molecular weight of benzene in both the solutions and justify your result.(Kb(acetone) = 1.7 KKgmol-1, Kb(benzene) = 2.6 KKgmol-1).

b)Glycerine, Glycol and methyl alcohol sell at the same price per Kg. Which would be cheaper for preparing an antifreeze solution for the radiator of an automobile? 3

20 i)With the help of crystal field theory predict the

number of unpaired electrons in [Fe(CN)6])4- and

[Fe(H2o)6]2+ complexes.

ii) The formula Co(NH3)5CO3Cl could represent a carbonate and a chloride. Give IUPAC names for them.3

OR

a) Give 2 limitations of valence bond theory.

b) Explain the d orbital splitting in an tetrahedral crystal field with the help of a diagram.

21a) A big irregular shaped vessel contained water, the conductivity of which was 2.56x10-5S/cm. 500g. of NaCl was then added to the water and the conductivity after the addition of NaCl was found to be 3.10x10-5S/cm. Find the capacity of vessel if it is completely filled with water.(Consider that the dilution is infinite. Limiting molar conductivity of NaCl=149.9Scm2/mol. Mol.mass of NaCl=58.5) 3

22. a) Explain the thermodynamics involved in choosing a reducing agent for a particular reaction. Give one example to substantiate your answer.

b)Give an example for the extraction of an element based on oxidation. 3

23. Account for the following

a)Haloalkanes undergo nucleophilic substitutions while haloarenes undergo electrophilic substitution.

b)Haloalkanes react with KCN form alkylcyanides while isocyanides are formed with AgCN.

c)Dipolemoment of chlorobenzene is lower than that of cyclohexyl chloride. 3

24. (a)Write short notes on primary, secondary, tertiary and quarternary structure of proteins.

(b)What happens when glucose is treated with

(i) aq.Br2

(ii) HNO3 3

25. (a)Illustrate the chain initiation step in the mechanism of addition polymerization.

(b)Distinguish between homopolymers and copolymers with examples. 3

26. (a)why does PCl5 exist in solid state at room temperature?

(b)Deduce the structure of ClF3 using VSEPR theory.3

27. I.Explain what is observed when:

a. an emulsion is subjection to centrifugation.

b. direct current is passed through a colloidal sol.

II.Write a chemical equation showing the preparation of a positive sol. 3

28. (a) A first order reaction has k=1.5x10-6 per second at 2400C. If the reaction is allowed to run for 10 hours, what percentage of the initial concentration would have changed to products? What is the half life period of this reaction?

(b)A 1st order reaction is 50% complete in 30 minutes at 270C and in 10 min. at 470C.Calculate

(i) rate constant for reaction at 270C and 470C.

(ii) energy of activation for the reaction. 5

OR

Two reactions i) Aà products ii) Bà products, follow first order kinetics. The rate of the reaction (i) is doubled when temperature is raised from 300K to 310K. The half life for this reaction at 310K is 30 minutes. At the same temperature B decomposes twice as fast as A. If the energy of activation for the reaction (ii) is half that of reaction (i), calculate the rate constant of reaction (ii) at 300K. 5

29. Account for the following.

(i) PH3 is a weaker base than NH3.

(ii) SF6 exists but SH6 does not.

(iii)ClF3 exists but FCl3 does not.

(iv) H3PO3 is diprotic acid.

(v) ICl is more reactive than I2. 5

OR

Assign reason for the following

i) Concentrated nitric acid turns yellow on exposure to sunlight.

ii) The negative value of electron gain enthalpy of Fluorine is less than that of Chlorine.

iii) SF6 is used as a gaseous electrical insulator.

iv) HI is a stronger acid than HF.

v) pKa value of HOCl is higher than that of HClO2.

30. (a)An organic compound (A) with the molecular formula C9H10O forms 2,4 –DNP derivative, reduces Tollen’s reagent to get(B).On vigorous oxidation it gives 1,2-benzene dicarboxylic acid. Give the structures of A and B.

(b)Convert

(i) Acetophenone to 2-phenyl-2-butanol.

(ii) Propene to acetone.

(iii)Propanoic acid to prop-2-enoic acid. 5

OR

An organic compound (A) of molecular weight 140.5 has 68.32% carbon, 6.4% Hydrogen and 25.26% Chlorine. Hydrolysis of (A) with dilute acid gives compound (B). Compound (B) can be oxidized under mild conditions to compound (C) C8H8O. Compound (C) forms phenyl hydrazone (D) and gives a positive iodoform test. Deduce the structures of (A)to(D). 5